The present application relates to a sealing ring, particularly for sealing articulated pipe connections, such as, in particular, a highly heat resistant sealing ring for sealing articulatedly connected exhaust pipes, the sealing ring having at least one jacket face which serves as a slide surface and is made of a material containing pressed together fibers and sliding agents.
It is known, for example from DE-GM No. 1,736,840, to articulatedly join the pipe ends of an exhaust pipe and an exhaust gas manifold so as to avoid a transfer of vibrations coming from the engine. For this purpose, a pipe coupling system is used which operates according to the known ball-and-socket principle in which the points of connection of the pipes are designed as matching ball segment and ball socket segment, respectively, so that a certain angular mobility, or relative movement, between the pipes is permitted. The sealing ring connected therebetween is adapted to the outline of the joint and at least one of its jacket faces is given the outline of the matching ball segment or ball socket segment. It thus performs the function of a slide bearing for the pipes.
In view of the functions to be performed, such sealing rings are made of anti-friction materials. According to DE-OS No. 2,829,333, DE-PS No. 2,845,949 and DE-OS No. 3,107,920, such materials today are preferably compressed anti-friction materials with embedded, relatively long metal fibers for reinforcement. The metal fibers employed, according to DE-PS No. 2,845,949, are advisably long fibers so that the rings have sufficient strength. According to DE-OS No. 2,829,333, the metal fiber skeleton is correspondingly made of a steel wire fabric which has been wound or folded onto an appropriately shaped core and, after coating with graphite plate material, is pressed into the desired shape. However, in such sealing rings, the inserted wire fabric is relatively rigid. Wires may break, particularly at the points where the wire fabric is folded, and may penetrate the graphite layer. These wire tips may then produce wear traces on the slide faces of the pipes, ultimately resulting in destruction of the pipes.
For that reason, DE-OS No. 3,107,920 employs embedded metal fiber wool instead of embedded wire fabrics. Thus, substantially thinner metal fibers can be used and with the irregular orientation of the metal fibers, the danger of the fibers pressing through and thus causing wear on the sealing surface is substantially avoided.
The drawback of all of the sealing rings disclosed in these three patents, however, is their costly, multistage manufacture. Initially the sealing ring skeletons must be shaped, possibly with prepressing, from the metal fabrics or metal fiber wool balls, then the metal skeleton is saturated and coated with the solid sliding agent which is possibly present in suspension, and only then is the ring pressed in a mold to attain the desired contour.
As a result of the method employed to manufacture the sealing ring, the sliding agent is nonuniformly distributed over the cross section of the sealing ring and is applied primarily as a coating to the surfaces of the sealing ring. However, such coatings adhere only poorly to the metal fiber skeleton and break relatively easily, so that the layers may break or chip off. The then exposed fibers and wires may produce wear damage at the sealing faces of the pipes and this may possibly develop into major corrosion damage. Primarily during engine operation, the relatively long fibers fray over their entire fiber length so that gradually the entire sealing ring is destroyed.